This invention relates to the recovery of gold from carbon fines.
Carbon fines are produced when carbon, which is used in a carbon-in-leach (CIL) or carbon-in-pulp (CIP) process for the recovery of gold, is broken. Typically, these fines, loaded to some extent with gold, exit from a last adsorption stage of the process and are then lost.
In some plants the process material is passed through an “adsorbent trap screen” prior to pumping the resultant slurry to a slimes dam. The fine adsorbent which is recovered contains some gold that was loaded in the adsorption circuit. Carbon losses can vary from 10 to 60 g/t of processed ore. This carbon can contain from 100 g to 1500 g of gold per ton.
Gold recovery from carbon fines is normally done by combustion followed by cyanidation of the ash. The combustion process is expensive and inevitably results in some gold losses. Carbon dioxide emissions caused by the combustion process are an adverse environmental factor.
Other processes which have been considered include the following: microwave-augmented ashing of carbon fines followed by cyanidation; elution of gold-containing fines with NaCN at an elevated temperature; and the use of a cyanide solution to slurry the gold-containing fines and leach gold, and then a transfer of the gold from the fines to coarser carbon.
An object of the invention is to provide a process for the recovery of gold from carbon fines at a relatively low temperature, at low cyanide and caustic concentrations, and at atmospheric pressure. Preferably the process should allow for gold recovery to be implemented on site, thereby avoiding the cost of transport to a toll treatment facility.